On 2/2/26 12:36, Jordan Niethe wrote: > A future change will remove device private pages from the physical > address space. This will mean that device private pages no longer have > normal PFN and must be handled separately. > > Prepare for this by adding a PVMW_DEVICE_PRIVATE flag to > page_vma_mapped_walk::flags. This indicates that > page_vma_mapped_walk::pfn contains a device private offset rather than a > normal pfn. > > Once the device private pages are removed from the physical address > space this flag will be used to ensure a device private offset is > returned. > > Reviewed-by: Zi Yan <[email protected]> > Signed-off-by: Jordan Niethe <[email protected]> > Signed-off-by: Alistair Popple <[email protected]> > --- > v1: > - Update for HMM huge page support > v2: > - Move adding device_private param to check_pmd() until final patch > v3: > - Track device private offset in pvmw::flags instead of pvmw::pfn > v4: > - No change > --- > include/linux/rmap.h | 24 ++++++++++++++++++++++-- > mm/page_vma_mapped.c | 4 ++-- > mm/rmap.c | 4 ++-- > mm/vmscan.c | 2 +- > 4 files changed, 27 insertions(+), 7 deletions(-) > > diff --git a/include/linux/rmap.h b/include/linux/rmap.h > index daa92a58585d..1b03297f13dc 100644 > --- a/include/linux/rmap.h > +++ b/include/linux/rmap.h > @@ -921,6 +921,8 @@ struct page *make_device_exclusive(struct mm_struct *mm, > unsigned long addr, > #define PVMW_SYNC (1 << 0) > /* Look for migration entries rather than present PTEs */ > #define PVMW_MIGRATION (1 << 1) > +/* pvmw::pfn is a device private offset */ > +#define PVMW_DEVICE_PRIVATE (1 << 2) > > /* Result flags */ > > @@ -939,14 +941,32 @@ struct page_vma_mapped_walk { > unsigned int flags; > }; > > +static inline unsigned long page_vma_walk_flags(const struct folio *folio, > + unsigned long flags) > +{ > + if (folio_is_device_private(folio)) > + return flags | PVMW_DEVICE_PRIVATE; > + return flags; > +} > + > +static inline unsigned long folio_page_vma_walk_pfn(const struct folio > *folio) > +{ > + return folio_pfn(folio); > +} > + > +static inline struct folio *page_vma_walk_pfn_to_folio(struct > page_vma_mapped_walk *pvmw) > +{ > + return pfn_folio(pvmw->pfn); > +} > + > #define DEFINE_FOLIO_VMA_WALK(name, _folio, _vma, _address, _flags) \ > struct page_vma_mapped_walk name = { \ > - .pfn = folio_pfn(_folio), \ > + .pfn = folio_page_vma_walk_pfn(_folio), \ > .nr_pages = folio_nr_pages(_folio), \ > .pgoff = folio_pgoff(_folio), \ > .vma = _vma, \ > .address = _address, \ > - .flags = _flags, \ > + .flags = page_vma_walk_flags(_folio, _flags), \ > }
That's all rather horrible ... I was asking myself recently, why something that is called "page_vma_mapped_walk" consume a pfn. It's just a horrible interface. * DEFINE_FOLIO_VMA_WALK() users obviously receive a folio. * mm/migrate_device.c just abuses page_vma_mapped_walk() to make set_pmd_migration_entry() work. But we have a folio. * page_mapped_in_vma() has a page/folio. mapping_wrprotect_range_one() and pfn_mkclean_range() are the real issues. They all end up calling page_vma_mkclean_one(), which does not operate on pages/folios. Ideally, the odd pfn case would use it's own simplified infrastructure. So, could we simply add a folio+page pointer in case we have one, and use that one if set, leaving leaving the pfn unset? Then, the pfn would only be set for the mapping_wrprotect_range_one/pfn_mkclean_range case. I don't think device-private folios would ever have to mess with that. Then, you just always have a folio+page and don't even have to worry about the pfn? -- Cheers, David
